1. Field of Invention
This invention relates generally to tool utilization in a manufacturing production line and, more particularly, to minimizing costs by determining which machine tools can be turned off during a down-turn period for maximum savings and minimum increase in cycle time.
2. Description of Related Art
In a large manufacturing foundry today, many complex processes are frequently used to produce a product. This is especially true in the semiconductor industry where many tools are necessary to produce the final chip product from a designer's data. These required tools are state-of-the-art and are frequently very expensive to build and run. The useful lifetime of these tools can be short due to changes in technology. To reduce the tool's cost, they must be used as near to maximum capacity as possible to amortize their cost over as long a useful life as possible. Still running, idle tools are not producing product and are costing money due to lost opportunity and unnecessary running costs. A dilemma often occurs on how to responsibly turn off some machine tools during these low production times to save operating costs yet keep fabrication timely and efficient. Unwise turning off of machine tools can lead to increased total building or cycle times of product runs, which in turn can lead to delays, bottlenecks, and unhappy customers.
Keeping tool utilization at a maximum can be very difficult in complex manufacturing environments where each product may need several machine tools to be built, and there can be several products being built concurrently that require different sequences of tools. Also, customers' designs might not need all the machine tools available. For example, a specific logic wafer tool may not be required for the next large order being processed. Currently, manufacturers commonly deal with any down-turn periods by turning off machine tools based only on predefined utilization percentages such as 90% or 95%. Unfortunately, this does not take into account cost savings per machine when turned off or cycle time impact.
A new method is needed that provides a way to objectively determine the optimum machine tools of the right type and quantity to be turned off for greatest operational cost savings with the least impact to increased cycle time. This invention provides this new method.
In U.S. Pat. No. 6,259,959 (Martin) it describes a process for determining the performance of components in a manufacturing line. Articles by the same author (D. P. Martin), “How the Law of Unanticipated Consequences Can Nullify the Theory of Constraints, Semiconductor Fabtech,” 7th edition, pp. 22-34 and “How Tool Characteristics Affect the Cycle Time and Capacity of a semiconductor Manufacturing Line,” Nov. 14, 1996 discuss X-factor theory. Katsutoshi Ozawa, Hideyuki Wada, and Tsuyoshi Yamaguchi in their article “Optimum Tool Planning Using the X-Factor Theory” reference these two articles as well as a third, “Breaking the Addiction to WIP: A Business Process for Driving Controlled Cycle-Time Improvement” by Greg Reichow, ISSM '98, when discussing using the X-factor theory in tool planning. In U.S. Pat. No. 5,826,040 (Fargher et al.) a method of planning a production schedule within a factory is disclosed. In U.S. Pat. No. 5,721,686 (Shahraray et al.) a method and apparatus for controlling and evaluating pending jobs in a factory is described. In U.S. Pat. No. 5,148,370 (Litt et al.) an expert system and method for batch production scheduling and planning is described.